The following relates to the illumination arts, lighting arts, and related arts.
Automotive indicator lighting must conform with applicable regulatory- and safety-related constraints, while also remaining cost-effective. In the highly competitive automotive market, a savings of a small fraction of a dollar per unit can translate into substantial cost savings. Additionally, automotive indicator lighting is an integral part of the overall design of the automobile, and accordingly should have an appealing appearance.
In the United States, automotive indicator lighting includes left and right taillight assemblies, as well as various optional or mandatory side and front signal light assemblies. Each taillight assembly includes a taillight that illuminates in red whenever the automobile headlights are on to enhance rear visibility of the vehicle. Each taillight assembly also includes a brake light that illuminates a brighter red (as compared with the taillight) to indicate application of the brakes, so as to warn following drivers of the vehicle braking operation. The brake light can be implemented either as a separate light or multi-filament assembly, or can be the same as the taillight but operated at a higher intensity. Still further, each taillight assembly includes a backup light, which must be white. Finally, each taillight assembly must include a turn signal light, which can be either red or yellow, but in either case must flash on and off. The basic requirements in Europe are similar, except that in Europe yellow turn indicator lights are mandatory.
The various signal components of the taillight assembly must be independently operable in order to simultaneously inform other road users of simultaneous vehicle conditions or events. For example, it may be that the automobile is backing up while simultaneously braking and turning. In such a case, the brake light must be on, the turn indicator light must be on, and the white backup light must be on, all simultaneously. Accordingly, the taillight assembly typically includes either three lights (in designs utilizing a combined taillight/brake light) or four lights (in designs utilizing a separate taillight and brake light).
The “red”, “white”, and “yellow” (sometimes also referred to as “amber”) colors are typically constrained by applicable regional regulations that specify more precisely the shade or hue or equivalent information for each indicator light color. These applicable regulations may be different in different geographical regions. As a result, an automobile that is “street legal” in Europe may fail to meet regulatory standards in the United States, or vice versa. These regulatory differences have spawned a lucrative market for high end automobile importers, which charge substantial fees for retrofitting the indicator lighting and other features of an imported automobile to comply with road regulations of the receiving country.
Even in the absence of regulatory constraints, the automobile manufacturer may wish to adapt the colors of the indicator lights to specific markets. For example, anecdotal evidence in the lighting industry suggests that in some countries illumination lamps that output a “cool white” light sell better than lamps producing “warm white” light; whereas, in the other countries lamps producing warm white light tend to outsell those producing cool white light. Similar local preferences may exist for automotive indicator lighting, influenced by factors such as “average” local visibility (typically high in a dry desert climate but lower in higher-humidity climates), the extent of artificial roadway lighting infrastructure, or so forth.
For vehicle manufacturers operating in a global marketplace, regional differences in regulatory standards and/or customer preferences complicate manufacturing and increase costs, as the manufacturer must employ different indicator light assemblies for automobiles intended for sale in various different geographical markets. This in turn means maintaining different stock keeping unit (SKU) lines for different regional taillight variations, which increases inventory, requires parallel supply lines for the different SKU lines, and restricts vehicle manufacturing and delivery flexibility.
Existing automobile indicator lights have additional deficiencies. For example, in spite of their complexity, the actual informational content provided by existing taillight assemblies is rather limited. A following driver is warned of braking by activation of the brake light, but is given no indication of whether the vehicle ahead is slowing down gently, or engaging in a panic stop. Indeed, existing commercial taillight assemblies provide no information about speed changes other than braking. Proposals exist to indicate “hard” braking by a mechanism such as blinking red brake lights, or blinking both amber turn indicators (if amber lights are used for the turn indicators). The former approach (blinking red brake lights) has the disadvantage that it could be confused with a slow braking event in which the driver taps the brake pedal several times (thus producing a “blinking” of the brake light).
One way to provide additional information is via light intensity changes. A change in the red light intensity is already used to indicate braking when the taillights are on. However, employing light intensity changes to convey additional information to other road users is problematic. One difficulty is that the visually perceived light intensity depends upon numerous factors besides the actual radiation output. These include: the intensity and source position of ambient lighting; atmospheric conditions; visual acuity of the perceiving road user; whether the perceiving road user is viewing directly or through a windshield or windscreen, and if the latter the transmissivity of the windshield or windscreen; the angle and distance from which the road user views the indicator light; and so forth. Using light intensity to convey analog information (such as how strongly the brakes are being applied, or the vehicle speed or acceleration rate) is therefore problematic, because it is difficult for other road users to gauge the absolute light intensity. Another problem with using variable light intensity to convey information is that the lowest end of the light intensity range may be visually imperceptible for some viewers.
Flashing a light on and off can also be used to provide information, as in a flashing turn indicator. Again, however, number of different kinds of information that can be intuitively conveyed by the flashing of lights is limited.
Another possible way to provide additional information is to provide additional indicator lights of different colors. For example, the inclusion of a rearward-facing green light to indicate acceleration was proposed at least as far back as the early 1940's (see Rodrick, U.S. Pat. No. 2,301,583). A green acceleration indicator light has not yet been adopted by any substantial geographical region, and some jurisdictions prohibit the use of colors other than red (and perhaps amber for turn signaling or white to indicate backup) in rearward facing vehicle signal lights. Thus, the adoption of green (or other “nonstandard” colors) is likely to occur, if at all, on a limited geographical basis.
The adoption of “new” signal lights, such as a green acceleration light, into existing vehicle signal lighting schemes is hindered by numerous factors. Cost is one issue. A typical taillight assembly already typically includes at least three different indicator lights (red, yellow, and white). Adding lights of additional colors would further add to vehicle manufacturing cost. The use of new signal lights is also hindered by government regulations, which can be slow to change and are highly region-specific. A new signal light must be “street-legal” in substantial geographical area (such as the United States, Europe, or so forth) in order to justify mass manufacturing of vehicles with the new signal light.
A relatively recent development in vehicle signal lighting has been a gradual replacement of incandescent signal lamps with light emitting diode (LED)-based signal lamps. For example, a red tail or brake incandescent lamp can be replaced by a red LED-based lamp, which provides faster light run-up time, higher electrical energy efficiency, improved operational lifetime and robustness against failure, and may reduce manufacturing cost. However, replacement of an incandescent lamp with an LED lamp does not reduce the multiplicity of different taillight assembly SKU lines needed for different geographical regions, and does not facilitate the adoption of new signal lights.
LED-based lamps have also been used to enhance aesthetic automotive design, for example by integrating LED lamps of different colors on a common substrate (see, e.g. Lawrence et al., U.S. 2005/0254240), and using flexible substrates to design LED taillight assemblies that conform with vehicle curvature (Chen, et al., U.S. Pat. No. 6,520,669). The use of an LED signal lamp that can selectively emit one of two or more different colors has also been proposed, so as to reduce the number of signal lamps. For example, Abbe et al., U.S. Pat. No. 6,714,128 discloses a “smart light” that includes a set of red LEDs and a set of amber LEDs with a controller that selectively operates either the red LEDs or the amber LEDs so as to enable the “smart light” to be selectively used as either a red taillight or brake light or as an amber turn indicator. This amounts to a tight integration of red and amber LED-based lamps on a common substrate together with integral control electronics.
However, these developments still do not reduce the multiplicity of different taillight assembly SKU lines needed to accommodate the various different regional signal light standards. Indeed, by integrating red and amber LED lamps on a common substrate, the number of different SKU lines required to accommodate different regional regulations or preferences may increase, since a difference in any one signal lamp of the integral assembly of signal lamps will require a new SKU line. These developments also do not facilitate the adoption of new signal lights.